Method of making a tapered thickness waveguide intergrated semiconductor laser

Abstract

Disclosed is a tapered thickness waveguide integrated semiconductor laser which has an active layer in which light emits and recombines; and an output tapered waveguide which facilitates an optical coupling to an optical fiber; wherein the active layer and the output tapered waveguide are monolithically integrated on a common substrate, and the output waveguide has a buried structure and the width and thickness of the output waveguide are smaller than those of the active layer. The active layer may be placed between two cladding layers each of which has a different conductivity type with each other, and the output tapered waveguide has a portion which contacts undoped cladding layer.

What is claimed is: 
     
       1. A method of making a tapered waveguide integrated semiconductor laser, said method comprising the steps of: a. growing, on a p-InP substrate, an undoped InP buffer layer, the substrate having a tapered waveguide region and a laser diode (LD) region; then   b. selectively diffusing Zn onto only said LD region to form an impurity diffusion region thereon; then   c. forming SiO2 insulating film thereon; then,   d. patterning said insulating film to form two substantially longitudinal mask regions separated by an interval portion, said mask regions each having a first mask width in said tapered waveguide region and a second mask width in said LD region, said first mask width being less than said second mask width, said interval portion having a first interval portion width in said tapered waveguide region and a second interval portion width in said LD region, said first interval portion width being less than said second interval portion width; then   e. forming, in sequence, an undoped InP spacer layer, a tapered waveguide layer and an active layer on said spacer layer, and an n-InP cladding layer, wherein a respective width of said tapered waveguide layer at an output end thereof is smaller than a respective width of said active layer, and wherein a respective thickness of said tapered waveguide layer at said output end thereof is smaller than a respective thickness of said active layer; then   f. removing a part of said mask regions in contact with a mesa stripe; then   g. growing a low-concentration n-InP buried layer, a high-concentration n-InP buried layer, and an unstrained n-InGaAsP contact layer; then   h. forming another insulating film thereon; and then   i. growing electrodes on only said LD region.   
     
     
       2. The method of making a tapered waveguide integrated semiconductor laser as set forth in claim 1, wherein said step b. comprises the step of using the open-tube diffusion technique such that dimethyl zinc (DMZ) and phosphine (PH3) are provided in a quartz reaction tube in which said substrate is placed, at a temperature of 600° C. for approximately 30 minutes to provide a doping concentration thereafter of approximately 5×10 17 . 
     
     
       3. The method of making a tapered waveguide integrated semiconductor laser as set forth in claim 1 wherein said step e. comprises the step of continuously growing said tapered waveguide layer and said active layer by a selective growth technique.